The present invention relates to a phased-array antenna, and more particularly to an array of stacked layers of dipole antennas, each layer tuned to a different frequency band to provide a phased array antenna for operation in different frequency bands.
The present invention utilizes multiple layer dipole arrays for separated frequency bands to achieve a multi-frequency band phased array antenna. An array of stacked dipoles achieves the performance in an operating band similar to the performance of a dipole array located over a ground plane. At the same time, the array of stacked dipoles is essentially transparent at lower frequency operations. Therefore, several layers of stacked dipoles each tuned to a different frequency band may be stacked to achieve desired multi-frequency multi-function operation.
The multi-frequency band antenna of the present invention may combine several radar operations using a common antenna aperture and has important applications in shipboard radars or airborne radars. The antenna of the present invention is compact and light weight and therefore offers excellent mobility. It has applications in the field of ground-based, mobile tactical radar systems. The capability of the radar is enhanced by using a lower frequency such as L-band for searching and a higher frequency such as C-Band or X-Band for tracking to take advantage of the target frequency response.
The arrays of the present invention may be used for surveillance radar, searching, tracking and communication simultaneously. Due to the frequency selective property of these arrays, the high frequency incident signal, is completely absorbed by the high frequency dipole array. This results in good isolation between the high frequency band and the low frequency band. For the low frequency signal, the insertion loss due to the high frequency array is small and the performance of the low frequency array can therefore be maintained. Separated feed boards are used for each frequency band. The feed boards are arranged in an interleaved fashion and result in a very compact packaging arrangement. Simultaneous multi-function operations may be achieved by using separated feeds. Band selection is also flexible. Furthermore, the electronic failure of one of the elements does not affect another element.
A multi-frequency array antenna consisting of interlaced waveguide radiating elements with operating frequencies in L, S and C-Bands has been described by J. E. Boyns and J. H. Provencher in "Experimental Results of a Multi-Frequency Array Antenna", IEEE Trans. on Antennas and Propagation, Jan. 1972, p. 106-107). The presence of the low frequency elements generates more significant grating lobes. Also, this prior an array does not have the frequency selective property of dipole pair arrays. Therefore, the high frequency incident signal will be coupled into the low frequency array and the isolation is poor.
Accordingly, it is a feature of the present invention to provide a phased-array antenna that operates in different frequency bands. Another feature of the invention is the provision of a multi-frequency band phased array antenna that has good isolation between the high frequency band and the low frequency band. Yet another feature of the present invention is to provide a phased array antenna for operation in different frequency bands that is compact and light in weight.